Genuine is the key there. You can never beat a boisterous person by being a prick with belittling or subjective questions. However, if you stick with concrete questions and examples then I have found it tends to disarm overly confident people!
This typically does two things: it exposes any subjective thoughts that have led them to being overconfident about the issue at hand and it actually helps to foster a relationship between them and myself bc it shows that I am legitimately trying to understand where they are coming from.